Platform/ARM/SgiPkg: Add support for remote numa memory nodes

On a multi-chip platform, there are memory nodes connected to the
remote chips that are usable. Setup memory descriptor HOBs for all
the remote memory nodes. Use the remote chip memory offset value to
determine the base address for these remote memory nodes.

A new PCD 'PcdChipCount' is added in the ArmSgiTokenSpace that a
platform can use to define the number of coherently connected chips
in a multi-chip package.

Signed-off-by: Aditya Angadi <aditya.angadi@arm.com>
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@arm.com>